1. Field of the Invention
The present invention relates generally to a flexible short pipe having a shock absorbing function and, more particularly, to a flexible short pipe which flexibly endures high pressure generated at a discharge port of a lifting pump as well as fatigue load, tensile load, and bending load generated by external force when a unit lifting pipe (or flexible pipe) which is used to collect manganese nodules from the floor of the deep sea and has a predetermined length is coupled to an adjacent unit lifting pipe (or flexible pipe).
2. Description of the Related Art
A variety of systems have been proposed to collect manganese nodules from the surface of the ocean floor. However, most of the systems include a collector which collects manganese nodules from the surface of the ocean floor, a lifting pump, a flexible pipe which couples the collector with the lifting pump and feeds the manganese nodules, mud and seawater from the collector, and a lifting pipe which moves slurry (manganese nodules, mud and seawater) from the lifting pump to a ship or platform.
As the demand for mineral resources increases all over the world, marine mineral resources have been coming into the spotlight as an alternative. Among them, manganese nodules found on the floor of the deep sea have a flat or spherical shape and are blackish brown and non-crystalline substances. When collecting the manganese nodule, it is soft. Meanwhile, when the manganese nodule dries, it becomes hardened and breaks easily.
The main constituents of a manganese nodule are manganese, iron, silica, and water, and the composition of minor constituents of the manganese nodule varies depending on the region. There are several theories about the formation of the manganese nodule: the precipitation of colloidal hydroxides, and the catalysis of iron oxide. The manganese nodule is buried in the deep sea at depths of from 4000 to 5000 m. It is reported that the growth rate of a manganese nodule is about 0.01 to 1 mm per every 1000 years.
As shown in FIG. 1, a system for mining the manganese nodule from the floor of the deep sea includes a collector which collects the manganese nodule from the floor of the deep sea, a flexible pipe which is coupled to the collector to transfer the manganese nodule to a lifting pump, a lifting pump which provides transfer force to the flexible pipe, a lifting pipe which is coupled to the lifting pump, and a marine onboard processor which is coupled to the lifting pipe and processes or stores the collected manganese nodule.
The flexible pipe coupling the collector with the lifting pump uses negative pressure generated in a suction port of the lifting pump as a driving force to feed the manganese nodule, mud and seawater from the collector to the lifting pump. That is, slurry is lifted up by the suction pressure of the lifting pump.
Thus, the flexible pipe maintains its pressure lower than the surrounding pressure and must be made of a material which can endure the pressure. Further, the material must bear fatigue load, longitudinal tensile load and bending load, similarly to the lifting pipe.
The lifting pipe is subjected to high positive pressure discharged from the lifting pump. Thus, the lifting pipe must also be made of a material which can endure high pressure generated in the discharge port of the lifting pump, as well as fatigue load, tensile load, and bending load.
FIG. 2 is a sectional view showing a riser which is used to collect oil from the sea and has a shape similar to that of the lifting pipe (or flexible pipe). Here, the riser has a layer structure made of a variety of materials so that it can resist pressure.
The lifting pipe (or flexible pipe) applied to the lifting system is problematic because the collector moves on the surface of the ocean floor. As shown in FIG. 3 which is a conceptual view of a conventional crude oil collecting system, in a marine oil collecting platform to which the conventional riser is applied, one side of the riser feeding oil from an oil collecting hole to the marine platform is secured to the bottom of the sea, so that there are few cases in which shocks are abruptly applied.
However, in the lifting system for lifting manganese nodules, the collector always moves, and a sudden movement occurring on a ship or a sudden change in ocean current affects the lifting pipe or the flexible pipe, hindering the smooth movement of the collector.
Further, in the marine platform for collecting oil, the riser or the like is not frequently taken up and installed. However, in the lifting system, the lifting pipe (or flexible pipe) must be frequently taken up to perform system checks or for other reasons.
FIG. 4 is a perspective view illustrating a conventional lifting pipe and a roller for rolling the lifting pipe. The roller is constructed to lift up and roll the lifting pipe (or flexible pipe) when it is required to be stored on the ship. Meanwhile, when it is required to lower the lifting pipe (or flexible pipe) to the bottom of the sea, the lifting pipe is unrolled from the roller.
Further, in order to allow the lifting pipe (or flexible pipe) to be smoothly lifted up or down, a guide device is used as an auxiliary device as shown in FIG. 5. This enables the lifting pipe (or flexible pipe) to be smoothly lifted up and down at the time of going into and out the sea.
However, a conventional coupling pipe for coupling lifting pipes (or flexible pipes) shown in FIGS. 4 and 5 is problematic because it has a simple coupling pipe structure having a linear shape, so that it insufficiently absorbs longitudinal shocks caused by sudden changes in a ship, collector, or seawater when the lifting pipe (or flexible pipe) enters the sea water and then performs a lifting operation, and has insufficient resistance to the force of a bending load and a torsional load, and thus a junction part between the coupling pipe and the lifting pipe (or flexible pipe) may be damaged. That is, the conventional coupling pipe is problematic in that it cannot flexibly cope with high pressure generated in the discharge port of the lifting pump as well as not with fatigue load, tensile load, and bending load.
That is, the movement of a ship being moved by seawater, tide or wind affects the lifting pipe secured to the ship. The ship continuously repeats pitching, rolling and yawing under the external force. In the case where the quantity of motion is small, load acting on the lifting pipe is only small longitudinal load generated by the movement of a short distance, so that a big problem does not occur. However, when an abrupt and large load is generated by unexpected causes, it acts as a longitudinal load on the lifting pipe, affects even the lifting pump, and additionally affects the collector because of the flexible pipe coupled to the lifting pump. Thereby, the collector may deviate from its trajectory or from the bottom of the sea, thus negatively affecting the smooth operation of the collector. The conventional coupling pipe for coupling lifting pipes or flexible pipes has low resistance to the above deformation because of structural problems.
Further, the conventional coupling pipe has no structure for enduring the bending and torsional load acting on the lifting pipe (or flexible pipe). Thus, when the lifting pipe is wound around the roller as shown in FIG. 4, a bending load acts on the lifting pipe (or flexible pipe), and any form of torsional load acts on the lifting pipe because it is long. Therefore, the coupling pipe for coupling the lifting pipes or flexible pipes is also subjected to the load, but the conventional coupling pipe is problematic in that it has no resistance to the deformation.